Wafer inspection and metrology systems help a semiconductor manufacturer increase and maintain integrated circuit (IC) chip yields by detecting defects that occur during the manufacturing process. One purpose of inspection and metrology systems is to monitor whether a manufacturing process meets specifications. Inspection and metrology system can indicate the problem and/or the source of the problem if the manufacturing process is outside the scope of established norms, which the semiconductor manufacturer can then address.
Evolution of the semiconductor manufacturing industry is placing ever greater demands on yield management and, in particular, on metrology and inspection systems. Critical dimensions are shrinking while wafer size is increasing. Economics is driving the industry to decrease the time for achieving high-yield, high-value production. Thus, minimizing the total time from detecting a yield problem to fixing it determines the return-on-investment for the semiconductor manufacturer.
Electron beam systems are used for wafer inspection and metrology. During operation, an electron beam system can electrostatically deflect an uninterrupted beam of electrons away from the optical axis and, thus, “switch” the electron beam “on” and “off.” This process is commonly referred to as “blanking.” Blanking is typically faster than stopping and starting the electron beam. Beam blanking may be a required function in electron beam systems used in, for example, lithography, testing, metrology, and inspection.
Blanking systems typically deflect a high-power electron beam onto an aperture diaphragm to blank the electron beam and prevent an electron beam from reaching a wafer. The high-density electron beam dissipates into a large amount of narrowly-distributed heat at the aperture diaphragm. Such intense heat on the aperture diaphragm causes many problems, including distorting the aperture or aperture diaphragm, damaging the aperture or aperture diaphragm, or burning the aperture diaphragm. The resulting heat to the aperture diaphragm also can shift the aperture and cause dimensional errors in stitching exposure patterns of a shaped electron beam.
Semiconductor manufacturers are demanding increased integration density and device proximity. An efficient and straightforward approach to meet these requirements is to use higher electron beam currents and higher electron beam energies. However, this approach leads to a serious problem. A megawatt per square centimeter power density in a focused electron beam apparatus can damage an aperture or aperture diaphragm during blanking or can burn an aperture diaphragm during blanking. A kilowatt per square centimeter power density in a shaped electron beam apparatus can cause pattern-stitching errors of exposure due to the heat expansion effect of the aperture or aperture diaphragm. Pattern-stitching errors can occur when, for example, sub-patterns cannot be stitched together precisely enough to meet electron beam lithography requirements, which can lead to integrated circuit malfunctions. Distortion, shifting, tilting, expansion, or other changes in shape to the aperture or aperture diaphragm increase the chance of a pattern-stitching error.
FIG. 1 is a plan view of an aperture diaphragm 201 with blanking deflector plates 202. The deflector plates in the −x-axis and −y-axis can be grounded, so a pair of unipolar blanking voltages (or currents) are applied on the deflector plates 202 in +x-axis and +y-axis. The focused electron beam is deflected in the aperture plane from the center 0 to position A in FIG. 1. Parking a focused electron beam with megawatt power density at the position A of the aperture diaphragm 201 in FIG. 1 can damage and even burn the aperture diaphragm 201 locally. The aperture diaphragm 201 may also be shifted laterally due to the tensile stresses resulted from uneven heating and/or temperature distributions. To reduce the local heat at position A in FIG. 1, the blanking system voltages Vx and Vy can be used to scan the beam from B to B′ back and forth at any polar angle θ, but the heat distribution is still rotationally asymmetrical around the aperture. The edge rim of the aperture diaphragm 201 can still be shifted, distorted, or damaged.
Therefore, what is needed is an improved electron beam apparatus and blanking technique.